k8s-amd64-n3: Add new K8s VM node

The three x86_64 Kubernetes nodes are starting to get full.  Adding
another VM will allow pods to be spread thinner.

datadisk-var.yaml

@@ -0,0 +1,11 @@
+variant: fcos
+version: 1.4.0
+
+storage:
+  filesystems:
+  - path: /var
+    device: /dev/vdb
+    format: ext4
+    wipe_filesystem: true
+    label: var
+    with_mount_unit: true

k8s-amd64-n3.yaml

@@ -0,0 +1,15 @@
+variant: fcos
+version: 1.4.0
+ignition:
+  config:
+    merge:
+    - local: common.ign
+    - local: datadisk-var.ign
+    - local: kubelet.ign
+
+storage:
+  files:
+  - path: /etc/hostname
+    contents:
+      inline: k8s-amd64-n3.pyrocufflink.blue
+    mode: 0644